1. Field of the Invention
This invention relates to a body fluid filter device for passing body fluid such as blood, ascites fluid, or thoracic fluid and separating the filtrate such as plasma.
2. Description of the Prior Arts
Among the devices heretofore developed and adopted for the filtration of body fluids, there is included that which is illustrated in FIG. 1. This device comprises a side plate 3 provided with a body fluid inlet 1 and a filtration residual fluid outlet 2, a side plate 5 provided with a filtrate outlet 4, a flow path forming plate 6 formed of a packing portion 6b of the shape of a rectangular frame and an empty space 6a enclosed with the packing portion 6b, a filter membrane 7, and a filtrate flow path forming plate 8 formed of a reticular filtrate flow path 8a and a packing portion 8b enclosing the filtrate flow path 8a, with the flow path forming plate 6, the filter membrane 7, and the filtrate flow path forming plate 8 piled up one on top of another and nipped liquid-tightly between the two side plates 3, 5. In this device, the body fluid such as blood which has flowed in through the body fluid inlet 1 is forwarded through the empty space 6a and filtered through the filter membrane 7. The concentrated blood corpuscles fraction of blood stopped on the filter membrane is withdrawn through the filtration residual fluid outlet 2 and the filtrate passed through the filter membrane is forwarded through the filtrate flow path 8a and discharged via the filtrate outlet 4.
From the viewpoint of the filtering property, however, this device has posed the following problem. It is well known that in devices of this kind the wall shear rate of the filter membrane increases and the filtering property is improved in proportion as the height of the body fluid flow path is decreased. In the device of FIG. 1, the height of the flow path in the empty space 6a serving to pass the body fluid can be decreased by decreasing the thickness of the flow path forming plate 6. Unfortunately, the filter membrane 7 is readily deformable, so that the body fluid flow path which is formed by the empty space 6a cannot retain a uniform height fixed by the thickness of the flow path forming plate 6 but, instead greatly fluctuates in height. For example, if the thickness of the flow path is set at 300 microns, an error of .+-.100 microns can occur. Therefore, even if the thickness of the flow path forming plate 6 is decreased extremely in this device, it is difficult to retain the desirable filtration amount and the amount varies widely.
With a view to eliminating this disadvantage of the conventional device, there has been proposed a filter device which comprises a slender manifold plate provided at one end thereof with a blood inlet and at the other end thereof with a blood outlet, filter membranes attached fast one each to the opposite sides of the manifold plate through the medium of interposed rubber gaskets incorporating 3 parallel channels, and collection plates provided with blood plasma vents and disposed so as to hold the filter membranes fast against the manifold plate [Trans. Am. Soc. Artif. Intern. Organs, XXIV, 21-26 (1978)]. Since the flow path has a great length compared with its width, this device entails a heavy pressure drop which gives rise to hemolysis and mars the practical worth of the device.
There has also been proposed an ultrafilter device particularly suitable for filtration of blood, which comprises at least one hollow filter chamber bordering a filter agent on one side thereof, provided thereunder with a filtrate discharge member, and incorporating an inlet for the medium subjected to filtration and an outlet for the medium concentrated by filtration (British Pat. No. 1,555,389). In this device, a substrate layer comprising a filter mesh fabric having openings of a side dimension not greater than 2.5 mm and a thickness between 0.1 and 0.5 mm is interposed at least between the filter agent and one chamber wall. This ultrafilter device however, has suffered from a disadvantage that it develops great negative pressure because it is used for ultrafiltration and gets clogged by addition of blood corpuscles or proteins to the membrane surface, because decreasing the thickness of flow path is limited on the structure, and wall shear rate is low. Consequently, there are some problems on blood injury such as residence of blood, hemolysis and coagulation on account of the clogging.
An object of the present invention, therefore, is to provide a novel body fluid filter device.
Another object of this invention is to provide a body fluid filter device capable of ensuring a desired filtration volume substantially without fluctuation of the filtration amount by providing an extremely thin blood flow path uniformly.